Catalyst. Substance that speed up a reaction without being changed in the process.

Catalyst, in chemistry, any substance that increases the rate of a reaction without itself being consumed.

A catalyst is any substance that speeds up a reaction without taking part in it so at the end of the reaction you have the same amount of catalyst as you started with.

Figure 1. Enzymes lower the activation energy of the reaction but do not change the free energy of the reaction. A substance that helps a chemical reaction to occur is called a catalyst, and the molecules that catalyze biochemical reactions are called enzymes.

(1) Ammonia is composed of one nitrogen and three hydrogen atoms so it is a compound. Therefore it can be broken down by chemical change.

Five factors typically affecting the rates of chemical reactions will be explored in this section: the chemical nature of the reacting substances, the state of subdivision (one large lump versus many small particles) of the reactants, the temperature of the reactants, the concentration of the reactants, and the …

Several factors affect the rate of diffusion of a solute including the mass of the solute, the temperature of the environment, the solvent density, and the distance traveled.

In general, increasing the concentration of a reactant in solution, increasing the surface area of a solid reactant, and increasing the temperature of the reaction system will all increase the rate of a reaction. A reaction can also be sped up by adding a catalyst to the reaction mixture.

A reversible reaction is a reaction in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. A and B can react to form C and D or, in the reverse reaction, C and D can react to form A and B. Weak acids and bases undergo reversible reactions.

Examples of reversible reactions

• Ammonium chloride is a white solid. It breaks down when heated, forming ammonia and hydrogen chloride.
• Ammonium chloride ⇌ ammonia + hydrogen chloride.
• The symbol ⇌ has two half arrowheads, one pointing in each direction. It is used in equations that model reversible reactions:

Here are some broad examples of chemical reactions in daily life:

• Combustion.
• Photosynthesis.
• Aerobic cellular respiration.
• Anaerobic respiration (including fermentation)
• Oxidation (including rust)
• Metathesis reactions (such as baking soda and vinegar)
• Electrochemistry (including chemical batteries)
• Digestion.

What are irreversible changes?

• Heating. Heating can cause an irreversible change. For example you heat a raw egg to cook it.
• Mixing. Mixing substances can cause an irreversible change.
• Burning. Burning is an example of an irreversible change.

A change which cannot be reversed to form the original substance (or substances) is called an irreversible change. If we burn a piece of paper, it changes into ash and smoke. So, the burning of paper is an irreversible change which cannot be reversed. …

Examples of irreversible changes

• Burning: When we burn a piece of paper or wood, it turns to ash and smoke. We cannot obtain paper and wood from the ash again.
• Cooking: We use heat for cooking, right? Once we cook our eggs, we cannot uncook them.
• Rusting of iron: You must have seen rusting of iron.

Irreversible changes are permanent changes that cannot be undone. Cooking, baking, frying, burning, mixing, rusting, heating are examples of irreversible changes.

A physical change is a change to a sample of matter in which some properties of the material change, but the identity of the matter does not. Physical changes can further be classified as reversible or irreversible. The melted ice cube may be refrozen, so melting is a reversible physical change.

N.B. If butter is melted to become a liquid, it is a reversible change because it can become solid again by freezing.

Cooking an egg is an irreversible change. The cooked egg cannot be turned back into a raw egg. The chemicals that make up the egg have been changed by cooking to make new substances.

When you are frying an egg, it’s a chemical change because the liquid part of the egg changes from liquid to solid. As it is frying, the liquid part of the egg changes colour from clear to white.

When chemical bonds are broken or formed, new particles are created. Therefore, frying an egg is a chemical change because it results in the formation of new particles.

Cooking the egg is an example of a chemical change.

U.S. Grade AA eggs have whites that are thick and firm; yolks that are high, round, and practically free from defects; and clean, unbroken shells. Grade AA and Grade A eggs are best for frying and poaching where appearance is important, and for any other purpose.

Rotting, burning, cooking, and rusting are all further types of chemical changes because they produce substances that are entirely new chemical compounds.

When you use high heat to boil an egg, it causes a chemical reaction between the yolk and the white that leaves a green film around the yolk. That film is iron sulfide, caused by iron in the yolk reacting with hydrogen sulfide in the white.

Try putting a broken emulsion in the blender, which can break down the dispersed phase into small droplets again. In a large bowl, start with a small amount of the continuous phase with an egg yolk and then gradually beat the broken sauce into it. In cooked egg emulsions, proteins can easily coagulate (curdle).

Most interactions with the cooking of eggs involve breaking old bonds in egg proteins through denaturation and forming new ones in their stead. When eggs are cooked, heat denatures the proteins and after the proteins bond with water, the eggs solidify and change color.